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  • Stall Speeds

    I'm getting a little confused when the lessons talk about stall speeds e.g.

    VS0 vs VSR0.

    What's the difference between the two? And why are some limits based on one and some on the other?

  • #2
    Re: Stall Speeds

    VSO is the stall speed or the minimum steady flight speed in the landing configuration. (The 'O' means landing configuration)
    VSRO means the stall reference speed in the landing configuration. It is approximately 6% faster than the stall speed itself and it cannot be less than VS1g, which is the speed where the aeroplane lift balances the weight at CLMAX.
    Under the certification rules Class B aircraft use the stall speed VS to define the relevant speed requirements.
    Class A aircraft use the VSR value for certification to define the relevant speed requirements, in particular VREF and V2min.
    Why the difference? They found that when they asked a group of 'average' pilots to find the stall speed of a particular aircraft under identical conditions the results were quite variable, but when they were asked to fly at CLMAX the speed was very consistent so as a consequence the Class A aircraft (basically airliners) use the stall reference speed for certification as it is a speed that can constantly be achieved.

    Colin

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    • #3
      Re: Stall Speeds

      Would it be correct to say then that VSR0 would be the stall speed in landing configuration (flaps down, gear down) if the aircraft was then flown straight and level?

      And that VS0 is the minimum speed that can be achieved in landing configuration when flying an approach?

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      • #4
        Re: Stall Speeds

        If you are at VSRO you are 6% above the stall speed itself. VSRO is not the stall speed only a reference speed above the stall.
        If you are at VSO then that is the minimum speed.
        Target VREF Class B is 1.3VSO
        Target VREF Class A is 1.23VSRO

        Colin
        Last edited by colin; 25-10-2012, 11:56. Reason: Data

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        • #5
          Re: Stall Speeds

          You are very clear as always Colin
          "For once you have tasted flight, your eyes will look up skywards, for there you have been and there you?ll always long to return...Leonardo Davinci"

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          • #6
            Originally posted by colin View Post
            Re: Stall Speeds


            Class A aircraft use the VSR value for certification to define the relevant speed requirements, in particular VREF and V2min.
            Why the difference? They found that when they asked a group of 'average' pilots to find the stall speed of a particular aircraft under identical conditions the results were quite variable, but when they were asked to fly at CLMAX the speed was very consistent so as a consequence the Class A aircraft (basically airliners) use the stall reference speed for certification as it is a speed that can constantly be achieved.

            Colin
            V2min ? .. Is it used for short field operations? Why not just V2 ? something less than V2 would at least effect the climb gradient, right?
            and about Clmax .. CLmax is referred to an airfoil. There are bunch of reasons and ways to achieve CLmax.. CLmax can be influenced even by a tropical rain (POF)

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